One of typical techniques applied to a data transmission system is a pre-emphasis technique. According to the pre-emphasis technique, when a frequency component of a signal attenuated during transmission is intensified in advance on the transmission side, the amplitude of the received signal may be increased on the reception side and an eye pattern may be secured. For example, Japanese Laid-open Patent Publication No. 2004-88693 discusses a circuit that generates a signal having a pre-emphasis waveform by branching a data signal into two signals, delaying one of the branched signals, and obtaining a difference between the delayed signal and the other signal.
However, the circuit according to the pre-emphasis technique may fail to reduce time-directional fluctuations caused in an output waveform of a light emitting element.